Re: systimer01.patch available for review.

[Alex Keahan <ak@xxxxxxxxxxxxx>]

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Joerg Sonnenberger wrote:
> On Thu, Jan 29, 2004 at 01:50:21PM -0600, Dave Leimbach wrote:
> 
>>How is it that a function written in assembly will create performance issues
>>over one written in C that uses inline assembly?  Is it some human factor?
> 
> 
> The compiler can't optimize it e.g. via inling the call. Consider the
> example of inb/outb which needs one instruction. if this are written
> as separate function, you need a call/ret pair, instructions to save and
> read the arguments etc. therefore this is way slower.


Actually, there's nothing fundamental to prevent the compiler from
inlining a function if the source is not in the file being compiled.

In fact, Sun's Forte C compiler can optimise and inline functions across
multiple source files.   With -xcrossfile, Sun CC analyses all the files
named on the command line as if they were a single source file.

Of course, this affects the way Makefiles are constructed, because
the files produced from cross-compilation must be used as one unit when
linking into a program.   In particular, if one function is changed, all
the files must be recompiled (due to possible inlining
interdependencies).

AK